1. Field of the Invention
This invention relates to the preparation of polyalphaolefin drag reducing agents, particularly the preparation of polymers and copolymers of alphaolefins that function as drag reducing agents.
2. Description of Related Art
The flow of liquid in a conduit, such as a pipe, results in frictional energy losses. As a result of this energy loss, the pressure of the liquid in the conduit decreases along the conduit in the direction of the flow. For a conduit of fixed diameter, the pressure drop increases with increasing flow rate. When the flow in the conduit is turbulent (Reynold's number greater than about 2100), certain high molecular weight polymers can be added to the liquid flowing in the conduit to reduce the frictional energy losses and alter the relationship between pressure drop and flow rate. These polymers, commonly referred to as drag reducing agents ("DRAs"), interact with the turbulent flow processes and reduce frictional pressure losses such that the pressure drop for a given flow rate is less, or the flow rate for a given pressure drop is greater. Because DRAs reduce frictional energy losses, increase in the flow capability of pipelines, hoses and other conduits in which liquids flow can be achieved. The use of DRAs can also decrease the cost of pumping fluids, the cost of equipment used to pump fluids, and provide for the use of a smaller pipe diameter for a given flow capacity.
Recognizing the desire to reduce frictional energy losses in the flow of liquid in pipes, a number of polymers, copolymers and methods for making polymers and copolymers have been proposed. For example, in one approach, a polymer is produced by the polymerization of an alphaolefin in a hydrocarbon solvent. The entire mixture, containing polyalphaolefin, solvent, and catalyst particles, is used without separation to make up dilute solutions of the polymer in crude oil or other hydrocarbons. In another approach, a composition of a polyacrylamide, water and a dispersing agent, which may be an anionic or nonionic surface active agent, is used. Earlier DRA polymer mixtures have certain shortcomings. For example, one of the problems associated with those DRA polymer mixtures is that the polymers, which are of high molecular weight, tend to be difficult to dissolve without degradation of the polymer and without significant reduction in molecular weight.
The present invention overcomes one or more of the shortcomings of earlier DRA polymer mixtures. In one aspect of this invention, a viscosity reducing agent that includes a substantially hydrophobic dispersant is introduced during the polymerization process. It is contemplated that the addition of the dispersant improves the bulk fluid properties and handling characteristics of the finished product and also improves the solubility of the finished product. It is further contemplated that through the process of including a dispersant during the polymerization process, a high molecular weight polyalphaolefin and a more uniform molecular weight distribution of the resulting polyalphaolefin may be achieved, thereby improving the solubility of the resulting polyalphaolefin drag reducing agent.